Prior to cutting a workpiece by means of an electrode wire, in a travelling wire EDM apparatus, it is necessary to thread the wire through a starting hole drilled in the workpiece. Threading of an electrode wire through a workpiece has been accomplished by diverse methods consisting generally in straightening the wire by exerting a pull on the wire, cutting the wire upstream of the workpiece, and feeding the cut end of the wire through the starting hole until the end of the wire is grabbed by the wire conveyor system.
However, in order to achieve a high machining speed and accuracy of the cut, the wire is subjected, during any cutting operations, to extreme thermal and mechanical stresses that can cause an accidental rupture of the wire in the middle of a cut. Such a rupture of the wire results in a prolonged work stoppage, more particularly if it occurs while the EDM apparatus is left unattended, for example, during the night. In order to avoid the economic waste caused by such work stoppages, it is necessary to provide for automatic re-threading of the wire immediately after its rupture. This operation is rather difficult to achieve due to the fact that the rupture of the wire has caused the wire to be out of shape and due to the fact that it is necessary to eliminate the unusable portion, or scrap portion, of the wire by cutting it off and evacuating the cut-off length of useless scrap wire. Until now there has been no practical solution proposed for disposal of the cut-off portion of the wire prior to starting the re-threading operation of the wire after an accidental rupture of the wire.